As shown in FIGS. 1 and 2, many motorcycles contain two-cylinder engines 10 in which the cylinders are arranged in a V-shaped configuration with the front cylinder 20 directly in front of the rear cylinder 30. This type of engine is commonly known as a V-type. V-type motorcycle engines are typically air-cooled. Harley-Davidson, Inc. of Milwaukee, Wis. manufactures and sells a popular line of motorcycles most of which are powered by air-cooled V-type two-cylinder engines. These motorcycles typically contain dual exhaust systems, each of which consists of two major parts—a header pipe and a muffler. The muffler is located at the end of the exhaust system and typically contains packing or baffles to reduce noise. The exhaust gases flow from the engine, through the headers, and then through the mufflers before being discharged to the atmosphere.
The exhaust ports of both the front and rear cylinder heads in the Harley-Davidson engines are located on the right side. In other words, when viewed from above facing forward, the exhaust ports are located to the right of an imaginary longitudinal line running through the wheels. Some of the models contain dual exhaust systems in which both systems are located on the right side of the motorcycle. Other models, including the Road King, Ultra Classic Electroglide, Softail, and Heritage, contain dual exhaust systems in which one muffler is located on the left side of the motorcycle and one muffler is located on the right side of the motorcycle. The exhaust gases from the front cylinder are easily routed from the exhaust port through a right header 40 to a right muffler 50. However, routing the exhaust gases from rear cylinder is not as straightforward.
Routing all the exhaust gases from the right side of the rear cylinder to a muffler on the left side of the motorcycle would require a lengthy and protruding header making a 180 degree bend. Harley-Davidson avoids such a header by using a rear equalizer header 60. The rear equalizer header carries the exhaust gases from the rear cylinder to both the right muffler and the left muffler 70. Due to the configuration of the equalizer header, most of the exhaust gases from the rear cylinder are conveyed to the right muffler, which already carries all the exhaust gases from the front cylinder. As a result, the right muffler carries a high percentage of the exhaust gases from the engine and the left muffler carries only a low percentage of the gases.
The result is acceptable aesthetically in that the motorcycle contains a right side exhaust system and a left side exhaust system. However, the imbalance in the dual exhaust system is undesirable functionally for three major reasons. First, the back pressure created by the exhaust system is much greater in the rear cylinder than in the front cylinder. Accordingly, the power produced by the two cylinders is not equal. Second, the right exhaust system wears out before the left exhaust system. Third, the sound coming from the dual exhausts is not balanced and alternating.
Accordingly, there is a demand for a method of modifying a motorcycle having a V-type two-cylinder engine and an imbalanced dual exhaust system to create a balanced dual exhaust system.